The concept of the Rega IOS MC stage was born during development work performed on the microphone amplifier used during the recording of Christine Collisters ‘Love’ album. The IOS is a ‘dual mono’ discrete symmetrical pre-amplifier using a high performance transformer input stage. It has been primarily designed to match the Apheta, but with its selectable loading and gain it will easily match any other cartridge.

The IOS combines the organic low noise ‘gain’ properties of the transformer and low noise high bandwidth discrete transistor circuitry. Housed in the Rega extruded aluminium case and fitted with full metal front panel it maybe our most complete product to date.

The function of a phono pre amplifier is to match the output from a pick up cartridge to the input of a line level amplifier. It is required to amplify the very low signals produced by the cartridge and also to equalise the in accordance with RIAA record cutting standard.

Rega believes that moving coil and moving magnet cartridges require different types of phono pre amplifiers to achieve optimum performance. The Ios is therefore dedicated to moving coil cartridges and avoids compromises.

We have avoided including any superfluous gadgets as they obstruct the signal path and degrade the sound quality.

The Rega Ios is a four stage all symmetrical amplifier. To provide optimum performance it is dedicated to amplifying the very low level signals that are generated by moving coil cartridges.

The first stage uses a 1:10 step-up transformer, which can be optimised to the cartridge by the selection of the correct loading and zobel DC resistance correction network connected across the MC transformer secondary.

The second stage is symmetrical compound pair class A amplifier, using paralleled low noise Hitachi transistors in the input stage. This drives the passive high frequency part of the RIAA equalisation stage.

The third stage is a symmetrical class A differential amplifier with a common base driver stage; this is also used as the active amplifier in the low frequency part of the RIAA equalisation stage.
The fourth stage is the active filter, this configuration uses the same circuit as found in the second stage. The filter element uses a very high bandwidth operational amplifier gyrator as the simulated inductance part of the tuned filter.

The power supply is a using fast diodes and a low noise voltage reference. Each stage has it’s own localised power supply, and LED referenced current generators.

Very high quality, polyproplene capacitors have been used in the signal path. 1% tolerance polypropylene capacitors are used in the RIAA EQ stages and audio grade capacitors are used in the rest of the circuit.

• General conditions
• Generator source resistance 15
• Load set to 100 & DC resistance set to 15 (Apheta)
• Output load resistance 100K
• Filter Off (unless otherwise stated)
• Input sensitivity for 200mV output 61uV - 70dB gain setting I
• 118uV - 64dB gain setting II
• Gain input to output 64dB Minimum
• 70dB Maximum
• Input load 50, 100, 150, 300 & 400
• DC resistance (Zobel network) 5 to 7.5 (6.25 nominal)
• 7.5 to 10 (8.75 nominal)
• 10 to 12.5 (11.25 nominal)
• 12.5 to 15 (13.5 nominal)
• 15 (Apheta)
• MC Transformer Sowter 8055
• Input overload @ 1KHz 8.7mV - 64dB gain setting
• 4.5mV - 70dB gain setting
• Maximum output level 14.7V RMS
• Rated output level 200mV